Flutter - 需要 2 个必需参数，但找到 0 个
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【中文标题】Flutter - 需要 2 个必需参数，但找到 0 个【英文标题】：Flutter - 2 required argument(s) expected, but 0 found 【发布时间】：2019-02-04 15:45:59 【问题描述】：我正在创建一个双 listView 应用程序，到目前为止运行良好，但我遇到了一个似乎无法修复的问题。
我收到错误消息[dart] 2 required argument(s) expected, but 0 found.
在我看来，这应该很容易解决，我认为我只需要改变......
body: _cryptoWidget(),
到...
body: _cryptoWidget(currency, color),
这不起作用，我仍然收到上述错误。
这是我用来激发错误的代码；
import 'package:flutter/material.dart';
import 'background.dart';
import 'package:flutter/foundation.dart';
import 'package:cryptick_nice_ui/data/crypto_data.dart';
import 'package:cryptick_nice_ui/modules/crypto_presenter.dart';
class HomePage extends StatefulWidget
@override
_HomePageState createState() => new _HomePageState();
class _HomePageState extends State<HomePage> implements CryptoListViewContract
CryptoListPresenter _presenter;
List<Crypto> _currencies;
bool _isLoading;
final List<MaterialColor> _colors = [Colors.blue, Colors.indigo, Colors.red];
List<String> items = [
"Item 1",
"Item 2",
"Item 3",
"Item 4",
"Item 5",
"Item 6",
"Item 7",
"Item 8"
];
_HomePageState()
_presenter = new CryptoListPresenter(this);
@override
void initState()
super.initState();
_isLoading = true;
_presenter.loadCurrencies();
@override
Widget build(BuildContext context)
return new Container(
decoration: new BoxDecoration(
color: const Color(0xFF273A48),
),
child: new Stack(
children: <Widget>[
new Scaffold(
appBar: new AppBar(
title: new Text("cryp"),
elevation: 0.0,
backgroundColor: Colors.transparent,
),
backgroundColor: Colors.transparent,
body: _cryptoWidget(),
)
],
),
);
Widget _cryptoWidget(Crypto currency, MaterialColor color)
final _width = MediaQuery.of(context).size.width;
final _height = MediaQuery.of(context).size.height;
final headerList = new ListView.builder(
itemBuilder: (context, index)
EdgeInsets padding = index == 0?const EdgeInsets.only(
left: 20.0, right: 10.0, top: 4.0, bottom: 30.0):const EdgeInsets.only(
left: 10.0, right: 10.0, top: 4.0, bottom: 30.0);
_gethtmlUI();
return new Padding(
padding: padding,
);
,
scrollDirection: Axis.horizontal,
itemCount: items.length,
);
new Scaffold(
appBar: new AppBar(
title: new Text('hello'),
elevation: 0.0,
backgroundColor: Colors.transparent,
),
backgroundColor: Colors.transparent,
body: new Container(
child: new Stack(
children: <Widget>[
new Padding(
padding: new EdgeInsets.only(top: 10.0),
child: new Column(
crossAxisAlignment: CrossAxisAlignment.center,
mainAxisSize: MainAxisSize.max,
mainAxisAlignment: MainAxisAlignment.start,
children: <Widget>[
new Align(
alignment: Alignment.centerLeft,
child: new Padding(
padding: new EdgeInsets.only(left: 8.0),
child: new Text(
'Your Feed',
style: new TextStyle(color: Colors.white70),
)),
),
new Container(
height: 300.0, width: _width, child: headerList),
new Expanded(child:
ListView.builder(
itemBuilder:
(context, index)
_getCryptoUI(currency, color);
)
)
],
),
),
],
),
),
);
return new Container(
decoration: new BoxDecoration(
color: const Color(0xFF273A48),
),
child: new Stack(
children: <Widget>[
new CustomPaint(
size: new Size(_width, _height),
painter: new Background(),
),
],
),
);
Container _getHtmlUI()
return new Container(
decoration: new BoxDecoration(
borderRadius: new BorderRadius.circular(10.0),
color: Colors.lightGreen,
boxShadow: [
new BoxShadow(
color: Colors.black.withAlpha(70),
offset: const Offset(3.0, 10.0),
blurRadius: 15.0)
],
image: new DecorationImage(
image: new ExactAssetImage(
'assets/img_0.jpg'),
fit: BoxFit.fitHeight,
),
),
// height: 200.0,
width: 200.0,
child: new Stack(
children: <Widget>[
new Align(
alignment: Alignment.bottomCenter,
child: new Container(
decoration: new BoxDecoration(
color: const Color(0xFF273A48),
borderRadius: new BorderRadius.only(
bottomLeft: new Radius.circular(10.0),
bottomRight: new Radius.circular(10.0))),
height: 30.0,
child: new Row(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
new Text(
'hello',
style: new TextStyle(color: Colors.white),
)
],
)),
)
],
),
);
ListTile _getCryptoUI(Crypto currency, MaterialColor color)
return new ListTile(
title: new Column(
children: <Widget>[
new Row(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
new Container(
height: 72.0,
width: 72.0,
decoration: new BoxDecoration(
color: Colors.lightGreen,
boxShadow: [
new BoxShadow(
color:
Colors.black.withAlpha(70),
offset: const Offset(2.0, 2.0),
blurRadius: 2.0)
],
borderRadius: new BorderRadius.all(
new Radius.circular(12.0)),
image: new DecorationImage(
image: new ExactAssetImage(
"cryptoiconsBlack/"+currency.symbol.toLowerCase()+"@2x.png",
),
fit: BoxFit.cover,
)),
),
new SizedBox(
width: 8.0,
),
new Expanded(
child: new Column(
mainAxisAlignment:
MainAxisAlignment.start,
crossAxisAlignment:
CrossAxisAlignment.start,
children: <Widget>[
new Text(
currency.name,
style: new TextStyle(
fontSize: 14.0,
color: Colors.black87,
fontWeight: FontWeight.bold),
),
_getSubtitleText(currency.price_usd, currency.percent_change_1h),
],
)),
new Icon(
Icons.shopping_cart,
color: const Color(0xFF273A48),
)
],
),
new Divider(),
],
),
);
Widget _getSubtitleText(String priceUSD, String percentageChange)
TextSpan priceTextWidget = new TextSpan(
text: "\$$priceUSD\n", style: new TextStyle(color: Colors.black));
String percentageChangeText = "1 hour: $percentageChange%";
TextSpan percentageChangeTextWidget;
if (double.parse(percentageChange) > 0)
percentageChangeTextWidget = new TextSpan(
text: percentageChangeText,
style: new TextStyle(color: Colors.green));
else
percentageChangeTextWidget = new TextSpan(
text: percentageChangeText, style: new TextStyle(color: Colors.red));
return new RichText(
text: new TextSpan(
children: [priceTextWidget, percentageChangeTextWidget]));
@override
void onLoadCryptoComplete(List<Crypto> items)
// TODO: implement onLoadCryptoComplete
setState(()
_currencies = items;
_isLoading = false;
);
@override
void onLoadCryptoError()
// TODO: implement onLoadCryptoError
有关我在此应用中使用的其他文件（例如 crypto_data.dart）的更多信息，请参阅 this GitHub repo 我用于对我的代码的某些部分进行建模。
【问题讨论】：
错误行号？ body: _cryptoWidget(_currencies[0], _colors[0])，应该可以解决问题 @diegoveloper 这解决了问题，现在我可以加载应用程序，但现在除了我的自定义背景之外，页面上实际上没有加载任何内容。你能提出解决办法吗？ @DineshBalasubramanian 这个特殊错误现在已经修复，但它是第 57 行供参考。 修正你的逻辑，你需要一个 currentColor 和 currentCrypto 的变量 【参考方案1】：您收到错误[dart] 2 required argument(s) expected, but 0 found. 的原因是没有传递任何参数。您提供的另一个示例：_cryptoWidget(currency, color) - 您正在尝试传递一个与所需参数不匹配的列表。
如 cmets 中所述，您可以在这里为 List 定义索引以获取所需的值：_cryptoWidget(_currencies[index], _colors[index])
【讨论】：
感谢您的回复。尽管当我问这个问题时我的经验要少得多，但回想起来我真的看不出我是多么困惑。您的回答将在其他人的早期旅程中有所帮助。以上是关于Flutter - 需要 2 个必需参数，但找到 0 个的主要内容，如果未能解决你的问题，请参考以下文章
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